Who, what, when, where: Phenological trends of the Seedcorn Maggot Complex (Diptera: Anthomyiidae) in three vegetable crops in Southern Quebec

Abstract

In eastern Canada, the seedcorn maggot complex (SMC) includes three agriculturally important taxa: Delia platura biotypes H and N, and D. florilega. Because their larvae are morphologically indistinguishable, field-collected individuals are often grouped together despite differences in phenology and life history. Using larval collections from broccoli, green onion, and dry onion fields in Southern Quebec (2017-2022), we identified specimens via HRM analysis and characterized taxon-specific phenology and abundance using Bayesian hierarchical generalized additive models. In Allium crops, D. platura biotype N dominated early-season infestations (May), followed by a shift in early June towards increased abundance of biotype H and D. florilega. In broccoli, all SMC members appeared later, with overlapping abundance peaks in June. These results reveal strong crop-dependent phenological differences and underscore the need to treat SMC members as distinct biological entities in pest management. The implications for optimizing an emerging sterile insect technique (SIT) program for D. platura in Quebec are significant: field releases of sterile males should target early-season biotype N in Allium crops, followed by releases of both biotypes later in the season in broccoli to maximize control efficacy.